Fatty acid synthase (FAS) synthesizes palmitate and other fatty acids. In adults, FAS has not been thought to be physiologically important. This notion was challenged by our demonstration that FAS affects metabolism in several tissues by activating the nuclear receptor PPAR. In liver, FAS-dependent activation is mediated in part by a phosphatidylcholine species that serves as a PPAR ligand. FAS also drives a PPAR- independent signaling process. Endothelial FAS deficiency results in vascular dysfunction caused by impaired palmitoylation of endothelial nitric oxide synthase (eNOS). Addition of palmitate, the direct product of FAS, does not restore defective PPAR or eNOS signaling in the setting of FAS deficiency. Our findings suggest that FAS is compartmentalized within an integrated cassette generating signaling-competent lipids that could affect metabolic disease. The long-term objective of this application is to improve the health of people with diabetes and obesity by modulating FAS signaling functions. This project will test the hypothesis that FAS transmits physiological signals. These lipid signals are compartmentalized through discrete signaling nodes, chaperones, and covalent modification of FAS itself to impact metabolic disease. The specific aims are: 1. To implicate phosphatidylcholine transfer protein (PC-TP) as a chaperone involved in the binding of an FAS-dependent endogenous ligand for PPAR in the nucleus by comparing PC-TP-associated lipid spectra using PC-TP purified from livers of control mice and liver-specific FAS-deficient mice. 2. To determine if mice with tissue-specific inactivation of CEPT1 (a putative node for FAS signaling) in the liver and at the endothelium have phenotypes that mimic those of mice with tissue-specific inactivation of FAS. 3. To identify FAS-interacting proteins potentially involved in directing FAS to distinct cellular compartments and compartmentalizing its enzymatic product to discrete signaling nodes. 4. To determine if nutritionally regulated phosphorylation sites as well as other covalent modifications in FAS mediate FAS enzyme activity and cellular physiology. By establishing compartmentalized FAS as a mediator of physiological signals, this project could improve human health by identifying novel therapeutic targets for a wide range of metabolic disorders associated with diabetes and obesity.